Abu Dawud Book 2, Hadith Number 1336.
Chapter : On the number of rakahs of the prayer at night.
Narated By Abu Salamah b. ‘Abd al-Rahman : I asked ‘Aisha, wife of the Prophet (PBUH): How did the Apostle of Allah (PBUH) pray during Ramadhan? She replied: The Apostle of Allah (PBUH) did not pray more than eleven rak’ahs during Ramadhan and other than Ramadhan. He would pray four rak’ahs. Do not ask about their elegance and length. He then would pray four rak’ahs. Do not ask about their elegance and length. Then he would pray three rak’ahs. ‘Aisha said: I asked: Apostle of Allah (PBUH), do you sleep before observing witr? He replied: ‘Aisha, my eyes sleep, but my heart does not sleep.